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# Download Force and Newton`s First Law

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Transcript

Physics the study of the relationship between matter and energy Motion A change in position in a certain amount of time Motion is relative. To know you are moving, you must have a reference point Distance – how far you traveled Distance vs. Displacement The distance between the final position and starting position is displacement (Ex: hiking on a trail. The trail may be 1 mile long but you may only end up 300 ft from where you started) Speed Equation Speed – the distance traveled divided by the time needed to travel that distance SI Unit is meters per second (m/s) Speed = distance time D S T Practice (Make sure you use the proper units) If it takes you 3 hours to travel 60 miles, what is your speed?? If you are running 3 miles in 30 minutes, what is your speed? Constant speed vs. Average speed Constant speed – an object covers equal distances in equal amounts of time The speed of moving objects is not always constant Average speed: total distance total time Graphing Speed What is happening in the following graph? Velocity Velocity: Speed in a given direction You can be going the same speed but two different velocities Velocity = distance + direction time D V T Acceleration The change in velocity divided by the time the change occurs A = Velocity(final) – Velocity(initial) Time Acceleration is speeding up, slowing down or changing direction Stop Here!!! Force What causes an object to accelerate? A force is a push or pull exerted on an object Force is measured in Newtons (kg m/s2) In order for an object to speed up, slow down or change direction, a force has to act on that object Inertia is the object’s tendency to resist changing its motion. The more inertia, the harder it is to start moving or slow it down Total Force Sometimes, more than one force can act on an object at the same time. Those forces together will affect the object’s motion. Forces usually act in pairs with one force acting on either side of the object The resulting force that exists between two is the total force Unbalanced Forces When a total force acts on an object, they are said to be unbalanced. Unbalanced forces can cause an object to start moving, stop moving, or change direction. Balanced Forces Balanced forces exist when the total force is equal to zero. Balanced forces do not change an object’s motion Friction and Air Resistance Friction is the force between two objects in contact that resists motion between two touching surfaces It is what eventually causes things to slow down and stop Air Resistance is a form of friction between an object and air molecules Gravity Gravity is the pull that all matter exerts on other matter Gravity is dependent on the mass of an object and the distance between the two objects The greater the mass, the more gravitational pull it will have (i.e.: earth vs. moon) The greater the distance, the less gravitational pull it will have Mass vs Weight – weight is the amount of gravitational pull on a person. So on the moon, your mass would be the same but weight would be different Free Fall and Terminal Velocity When the only force acting on an object is gravity, the object is said to be in free fall On earth, this is 9.8 m/s2 - Gravity constant In the absence of air resistance, all objects on Earth accelerate at the same rate, regardless of their mass. An object reaches its terminal velocity when the force of gravity is balanced by the force of air resistance Gravity Demo Newton’s Laws Newton’s First Law of Motion “An object at rest will remain at rest and an object in motion will maintain its velocity unless it experiences an unbalanced force.” This is often times called the law of Inertia Newton’s Second Law of Motion “The unbalanced force acting on an object equals the object’s mass times its acceleration” F=ma Force is measured in Newtons (kg m/s2) Newton’s Third Law For every action force, there is an equal and opposite reaction force